Full featured data access arrangement for use with modems

ABSTRACT

A full-featured data access arrangement (DAA) for connecting a modem to a public switched telephone network (PSTN) includes a bridge current loop circuit, a line in use detection circuit, an off hook relay, a loop current sense circuit, and an extension/remote event detector circuit. The off hook relay is connected in series with the current loop circuit to enable the DAA to detect external off hook and on hook events when the modem is in an on hook state. The DAA is configured to detect the off hook and subsequent on hook status of an extension telephone at a location even though the modem and a handset sharing a line connector with the modem are both in an on hook state. The DAA is also capable of detecting an off hook state of an extension telephone even though the modem is in an off hook state. In addition, the DAA can detect when a remote telephone device that initiates an incoming call is placed on hook.

TECHNICAL FIELD

The present invention relates, generally, to data access arrangement(DAA) devices, sometimes referred to as direct access arrangementdevices, for connecting a telephone device to a telephone network and,more particularly, to a full-featured DAA configured to support evolvingtelephony industry standards.

BACKGROUND ART AND TECHNICAL PROBLEMS

The Telecommunications Industry Association (TIA) and the ElectronicsIndustry Association (EIA) from time to time promulgate non-bindingtechnical standards for equipment sold in the telecommunicationsindustry. While compliance with these standards by product manufacturersis generally voluntary, the practical importance of producing equipmentin compliance with TIA/EIA standards is becoming increasingly important.In addition, the Federal Communication Commission (FCC) from time totime publishes binding regulations governing the telecommunicationsindustry to ensure safety, compatibility, and to minimize problematicinterference among various electrical devices and components sold in thetelecommunications industry.

In particular, Part 68 of the FCC Guidelines, incorporated herein bythis reference, relates to such matters as, for example, the requirementthat telephones and other telephone devices be electrically isolatedfrom the telephone network to prevent shock, fire, and otherenvironmental hazards from effecting the users of such equipment. Inthis context, the term "telephone device" can refer to telephones,modems, personal computers (PCs), fax machines, telephone answeringmachines (TAM), and the like, which are typically connected to atelephone line through a conventional RJ-11 telephone jack.

Recently, TIA/EIA Standards Proposal No. 3131-A was approved andpublished as TIA/EIA-695 which relates to, inter alia, various functionsto be supported by data access arrangement (DAA) devices, also commonlyreferred to as direct access arrangement devices. In particular, a DAAis a device which connects a telephone device, e.g., a modem, to anRJ-11 type jack, to thereby provide an interface between the modem andthe Public Switched Telephone Network (PSTN). The DAA suitably includesan appropriate opto-electric or other isolation device to isolate thePSTN (which typically operates in the range of 42-200 volts) from themodem (which typically operates in the range of about 1 to 3 volts peakto peak). The transformer circuit within the DAA which performs thisvoltage step-down function is often referred to as the primarytransformer, or simply as a "T1" device.

One of the principle functions of a conventional DAA surrounds theability of the DAA to detect an incoming ring signal. When a ring signalis detected in a conventional telephone handset, the user can simplylift the telephone handset from the receiver, whereupon the telephone issaid to go "off hook". Upon assuming the off hook position, the "offhook" relay within the DAA closes, thereby establishing a connectionbetween the telephone handset and the telephone device which generatedthe incoming call. When the telephone call is finished and the userplaces the handset back onto the receiver, the handset is said to goback on hook, whereupon the off hook relay within the DAA is open,terminating the connection.

In a modem context, upon detection of a ring signal, the DAA may beconfigured to transmit a ring detect signal to a controller associatedwith the modem or with the PC with which the modem is associated,whereupon a control signal is applied to the DAA's off hook relay,closing the relay. Upon closure of the off hook relay, a datacommunications path is established between the modem and the telephonedevice which generated the incoming call.

Many modems in use today, particularly modems associated with PCs, alsoinclude a local handset connection, such that both the data modem andthe telephone handset are connected to the telephone network through asingle, shared RJ-11 phone jack or other interface device. In thiscontext, it will be understood that the term "telephone handset" caninclude audio speakers, a headset, a voice activated speaker phone, acondenser microphone, or virtually any other audio configuration whichpermits voice or audio transmission. Moreover, it will also beunderstood in the context of the present invention that the term "localhandset" or "local device" refers to a telephone or other device whichshares a common RJ-11 type device with a modem, whereas the term"extension handset" or "extension device" refers to a telephone devicewhich is connected to a common telephone line (for example, in anotherbedroom of the same home) but which has its own RJ-11 type phone jack(i.e., the extension telephone device does not share a common RJ-11connection).

DAAs for use with a modem having a local handset are generallywell-known, for example as described in Chapter 6 of the "K-SeriesDesign Manual" published by Silicon Systems, the entire disclosure ofwhich is hereby incorporated by this reference. Presently known DAAs,however, are unsatisfactory in several regards. For example, while apresently known DAA associated with a modem may detect an extensiontelephone device off hook condition while the modem is off hook, manyknown DAAs are unable to detect an extension device off hook conditionwhile the modem is on hook. Moreover, to the extent a presently knownDAA is able to detect when an extension device goes off hook while themodem associated with the DAA is on hook under certain circumstances,the DAA is unable to ascertain when the extension device goes back onhook.

A full featured DAA which overcomes the shortcomings of the prior art isthus needed.

The present invention provides a full-featured DAA for use with a modemwhich overcomes many of the shortcomings of the prior art.

SUMMARY OF THE INVENTION

The present invention provides methods and apparatus for interfacing aphone device with a telephone network in a manner which overcomes manyof the shortcomings of the prior art.

In accordance with a preferred embodiment of the present invention, aDAA circuit is provided which detects when an extension telephone devicegoes off hook while the modem associated with the DAA is on hook, aswell as detecting when the extension device goes back on hook. Theability of the subject DAA to detect when an extension device goes backon hook is particularly important, inasmuch as it permits a facsimile orother data packet which is desired to be transmitted to be queued andtransmitted from the queue once the extension telephone device goes backon hook.

In accordance with a further aspect of the present invention, when themodem with which the DAA is associated is in the off hook condition, theDAA is configured to detect when an extension telephone device goes offhook, and to report this event to the user of the PC to which the modemis associated. In this way, the user can be informed that the modemconnection has been terminated because of an extension off hookcondition, as opposed to other common causes for modem disconnections,including internet service provider (ISP) failure, line failure, localhard drive failure, or the like.

In accordance with a further aspect of the present invention, when themodem is in the off hook condition, its associated DAA may be configuredto detect when a remote telephone device (i.e., the telephone devicefrom which an incoming telephone call has been placed) is hung up. Thispermits a modem, for example operating in the TAM mode, to terminate theconnection when the remote telephone device hangs up, thus avoiding thefamiliar but annoying dial tone which is often inadvertently replayed bymany TAM users when checking their telephone messages, as a result ofthe recording device associated with the answering machine commencingits recording sequence immediately before the calling party hangs up.

In accordance with a further aspect of the present invention, many ofthe foregoing functions may be conveniently implemented in software,thereby providing an efficient, low cost, TIA/EIA compliant DAA usefulwith current and future generation modems, including but not limited tothe new 56 kbps modem technologies currently emerging, for example thenew 56K modem chip sets produced by Rockwell Semiconductor Systems ofNewport Beach, Calif.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The present invention will hereinafter be described in conjunction withthe appended drawing figures, wherein like numerals denote likeelements, and:

FIG. 1 is a schematic block diagram of an exemplary DAA circuitinterconnecting a modem hybrid circuit with an incoming telephone line;

FIG. 2 is a schematic, functional block diagram of an enhanced DAAcircuit illustrating an arrangement of voltage and current detectioncomponents which provides enhanced event detection functionality to aDAA;

FIG. 3 is a schematic block diagram of a single telephone line having aplurality of telephone extensions;

FIG. 4 is an exemplary schematic circuit diagram of a conventionalvoltage detection circuit;

FIG. 5 is a schematic circuit diagram of an exemplary line in usedetection circuit;

FIG. 6 is a graphical depiction of the output signal generated by theline in use circuit of FIG. 5;

FIG. 7 is a schematic diagram of a exemplary embodiment of a linecurrent sense circuit; and

FIG. 8 is a graphical representation of an exemplary output of the linecurrent sense circuit shown in FIG. 7.

DETAILED DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

Referring now to FIG. 1, a conventional DAA 10 suitably connects a modem12 to the Public Switched Telephone Network (PSTN), Private BranchExchange (PBX), or the like. As is known in the art, the incoming signalfrom the PSTN/PBX is typically carried on a pair of "wires" referred toas the tip and ring lines 18 and 20, respectively. Thus, the tip-to-ringvoltage is typically expressed as V_(tr).

Modem 12 suitably comprises a modem hybrid 14 and a voice hybrid 16 tofacilitate the transmission of both voice and data through the samemodem 12. Although modem hybrid 14 and voice hybrid 16 are illustratedschematically in FIG. 1 as separate functional units, those skilled inthe art will appreciate that the data and voice functions of modem 12may suitably be integrated in any desired manner.

With continued reference to FIG. 1, a preferred embodiment of thepresent invention is suitably implemented in the context of a modemwhich includes a modem (or data) hybrid component and a voice hybridcomponent, such that the single modem can support data, facsimile, andother non-voice transmissions through incoming lines 18 and 20, as wellas voice and other audio transmission through voice lines 22 associatedwith a local hand set 36. In this context, it will be understood thatlocal handset 36 is connected to the PSTN through an RJ-11 typeconnector which the handset shares with DAA 10. In accordance with aparticularly preferred embodiment, it will be appreciated that bothvoice and data is suitably transmitted to and from the PSTN through tipand ring wires 18 and 20.

More particularly, a voice relay circuit 24 is suitably configured topermit either the simultaneous transmission of voice and data throughthe implementation of the well-known SVD (simultaneous voice and data)function associated with conventional modems or, alternatively, voicerelay 24 may be configured to permit a transmission of data only orvoice only.

With continued reference to FIG. 1, a ring detect circuit 28 is suitablyconfigured to detect the presence of an incoming "call" through the PSTNfrom a remote telephone device, i.e., a remote modem, fax machine,telephone handset, or the like. When an incoming call is detected, ringdetect circuit 28 suitably sends a signal to modem 12, whereupon asignal may be applied to off hook relay 26 to thereby close the relayand accept the call. Once the call is accepted, the incoming AC signalis applied to modem 12, and a DC component of the incoming signal istransmitted through bridge circuit 30 to a DC current sink circuit 32.During a call connection, DC current sink 32 suitably consumes a DCcomponent of the incoming signal sufficient in magnitude to permit thedetection of the call connection by the local exchange carrier (LEC) orthe local Central Office (CO). When the call is terminated, i.e., whenoff hook relay circuit 26 is again opened, the DC component transmittedthrough bridge circuit 30 is essentially terminated, allowing the CO todetect the completion of the call.

With continued reference to FIG. 1, an event detection circuit 34 issuitably employed to monitor the magnitude of the loop current in DCcurrent sink circuit 32, to thereby detect an off hook condition of anextension telephone device (e.g., by detecting a change in the loopcurrent as a result of an extension off hook condition).

With continued reference to FIG. 1, many conventional DAAs areconfigured such that off hook relay circuit 26 is in series with theincoming telephone line, as shown in FIG. 1, as opposed to locating theoff hook relay within the current sink loop connected to bridge 30.Consequently, for those DAAs wherein the off hook relay circuit islocated in the incoming telephone line as shown in FIG. 1, the DAA istypically only capable of detecting an extension telephone off hookcondition when the modem is in the off hook condition (i.e., when offhook relay 26 is closed). Stated another way, it is necessary toestablish a modem connection as a precondition to the ability of the DAAto detect certain external events, such as the off hook condition of anextension device, a hang up condition of a remote telephone, or thelike. Moreover, the configuration of the off hook relay as shown in FIG.1 generally precludes the DAA from detecting many of these importantexternal events when the computer associated with the modem is off or ifa modem connection does not exist.

Referring now to FIG. 2, an improved DAA 202 in accordance with thepresent invention suitably includes a caller ID relay 208, a ring detectcircuit 220, a bridge 210, a bridge current loop circuit 222, a line inuse detection circuit 212, an off hook relay 214, a DC current sinkcircuit 216, a loop current sense (LCS) circuit 217 and anextension/remote event detector circuit 218. In addition to performingmany of the functions set forth in TIA/EIA-695, DAA 202 suitablysupports many of the existing functions associated with conventionalDAAs, such as isolating modem 204 and its associated local handset 224from the high voltage environment of the PSTN.

With continued reference to FIG. 2, off hook relay 214 is suitablyconnected in series with current sink loop 222, as opposed to beingdisposed in series with the incoming tip and ring lines, as is the casewith may prior art DAAs. This improvement has substantial implications,as discussed in greater detail below, in that it permits DAA 202 todetect various external events even when a modem connection is notextant (i.e., even when off hook relay 214 is open).

With continued reference to FIG. 2, those skilled in the art willappreciate that a caller ID (CID) signal is generally transmitted fromthe LEC between the first and second audible rings. In accordance with apreferred embodiment of the present invention, ring detect circuit 220is suitably configured to detect an incoming call, whereupon DAA 202 isadvantageously configured to capture the telephone number or otherindicia associated with the incoming call, via ring detect circuit 220,CID circuit 208, or through any other convenient mechanism. Once the IDof the incoming call is captured, it can be compared with a look uptable stored in memory associated with the modem, or otherwise evaluatedto determine whether the modem desires to accept the incoming call. Forexample, a list of destinations from which the modem desires to acceptcalls, or a list of destinations from which the modem desires to rejectcalls, or both, may suitably be compiled and stored in memory, forexample in the form of a look up table. When the ID of the incoming callis captured and compared to the look up table, the call may be acceptedor rejected, as desired.

If the call is to be accepted, the controller (not shown) associatedwith modem 204 sends an appropriate signal to CID circuit 208, therebyclosing the relay. The modem is also configured to transmit a signal tooff hook relay circuit 214 to close the relay and thereby establish thecall connection.

Once a call connection is established, bridge circuit 210 drops the linecurrent, and converts a portion of the incoming signal to DC, creating acurrent loop in current loop circuit 222 which is detectable by theCentral Office (CO), such that the CO can determine that the callconnection has been made. The remaining AC component of the incomingsignal is suitably applied to the modem hybrid circuit.

With continued reference to FIG. 2, DC current sink circuit 216 suitablycomprises a line current sense detector 217 for detecting an off hookcondition of modem 204, while circuit 226 suitably comprises a loopcurrent sense detector 227 for detecting an off hook condition ofhandset 224. In accordance with a particularly preferred embodiment, ifduring a modem connection the user desires to integrate voice into thetransmission, the user may press a suitable function key or otherwiseinteract with the modem (or its associated PC), for example bydepressing a predetermined key on the keyboard associated with the PC.In this way, the SVD function may be implemented, causing the voicerelay circuit 228 to integrate the handset into the modem connection.

In accordance with a particularly preferred embodiment, when LCS circuit226 detects the off hook condition of local handset 224, DAA 202suitably signals the modem controller to initialize the SVD function.

In a particularly preferred embodiment, line in use circuit 212 issuitably implemented using a TMOS or other suitable, inexpensiveelectronic component. This is in contrast to prior art systems, whichtypically detect an off hook condition of an extension telephone deviceusing a comparator circuit. By integrating the TMOS circuit into line inuse detection circuit 212, the need for a comparator circuit and itsassociated high cost is also eliminated. Moreover, the use of a TMOS orsimilar device draws very little current, for example on the order of 5microamps, which further facilitates compliance with FCC Part 68.

In accordance with an alternate embodiment of the present invention, thesubject DAA may be configured to detect an off hook condition of anextension telephone device even when the modem remains off hook.Referring now to FIG. 3, an incoming call from the Central Office (CO)302 is suitably applied to a single telephone line 304 associated with ahome, small office, or the like. In the illustrated embodiment, thesingle phone line 304 suitably has associated therewith a plurality ofextensions, for example a first extension 306 located in a bedroom, asecond extension 308 located in the kitchen, and a third extension 310which is suitably dedicated to a PC having a local handset 312associated with the PC. As discussed above, the PC and local handset 312suitably share a common RJ-11 connection to the telephone line 304. Whenboth the local modem and local handset associated with extension 310 arein the on hook condition, conventional DAAs associated with the modem atextension 310 are typically incapable of detecting an off hook conditionof an extension handset, for example, in the kitchen. In order to detectan off hook condition on an extension telephone device while the localmodem and local modem handset remain on hook, it may be desirable toincorporate a voltage detector circuit, for example as shown in FIG. 4,to detect a reduction in voltage (or current) as a result of anextension off hook condition. More particularly, an extension off hookdetector circuit 404 suitably comprises a storage capacitor 406corresponding to an analog memory component, a detector circuit 408having an output signal 410 associated therewith, and suitablyconfigured to detect the tip-to-ring voltage associated with telephoneline 304, which voltage is known to drop upon the occurrence of an offhook condition of any extension telephone device. However, it will beappreciated that sensing circuits such as that shown in FIG. 4 are notreadily capable of detecting when the extension telephone device goesback on hook and, hence, such circuits are of limited utility.

Returning now to FIGS. 2 and 5-8, a number of particularly preferredembodiments of the present invention suitably provide apparatus andtechniques for detecting an off hook condition of an extension telephonedevice, as well as the return of that device to an on hook condition,regardless of whether the modem associated with the DAA is on hook oroff hook.

With reference now to FIGS. 2 and 5-6, line in use detection circuit 212is suitably configured to detect tip-to-ring voltage (or a scaledcomponent thereof, for example within current loop 222. Line in usecircuit 212 is also configured to generate an output signal 510 which,in the illustrated embodiment, is essentially a binary output signal.Output signal 510 is suitably applied to the modem controller (notshown) to indicate to the controller whether the line is in use, i.e.,whether any extension device is off hook, as described in greater detailbelow.

With continued reference to FIGS. 2 and 5-6, circuit 212 suitablycomprises respective first and second voltage divider resistors R1 andR2, respective first and second switches SW1 and SW2, respective currentpaths 504 and 506, and an opto-isolator element 502. It should beappreciated that the values of resistors R1 and R2 are suitably selectedto ensure that DAA 202 may be employed in conjunction with a widevariety of telephones, telephone lines, and telephone systems (i.e.,PBX, PSTN, public telephones, and the like) to effect a change in outputsignal 510 upon a drop in tip-to-ring voltage V_(tr). With specificreference to FIGS. 5 and 6, output signal 510 applied to the modemcontroller is suitably high when no extension devices are in the offhook condition, whereas output signal 510 is suitably low when anyextension (e.g., extension 306 or 308 in FIG. 3) is in the off hookcondition. In contrast to the voltage detection circuit illustratedschematically in FIG. 4, the line in use detection circuit 212 shown inFIG. 5 follows V_(tr) in essentially real time, i.e., without the delayoccasioned by capacitor 406. When no extensions are off hook, V_(tr) ishigh, such that SW1 is closed, causing current to flow through path 504.As a result, SW2 remains open, such that no current flows through path506. With no current flowing through path 506, the opto-element 502remains disabled, such that output signal 510 is pulled high. When anextension telephone device goes off hook, causing a drop in V_(tr), SW1opens, terminating the current flow through path 504. As a result, SW2closes, producing current flow through path 506. The current flowactivates opto-element 502, energizing the LED associated with theopto-element, such that output signal 510 is driven low. This phenomenais graphically illustrated in FIG. 6, where time t₁ corresponds to anextension telephone device going off hook, and the interval betweentimes t₁ and t₂ corresponds to the period in which an extensiontelephone device remains off hook.

In this way, the subject DAA set forth in FIG. 2 and as explained abovein conjunction with FIG. 5 is capable of communicating to the modemcontroller a signal (signal 510) any time an extension telephone devicegoes off hook, while modem 204 is on hook. Moreover, it will beappreciated that when the modem is off hook, i.e., during a modemconnection, the modem connection is typically terminated when anextension telephone device goes off hook. This is analogous to asituation where a user of a PC (i.e., PC 310 in FIG. 3) is involved inan online session (e.g., with an external ISP), and during the modemsession, someone else in the house unwittingly picks up a telephone inthe kitchen (extension 308) or in the bedroom (extension 306). As aresult, the modem connection is typically terminated, as distinguishedfrom the situation where handset 312 may go off hook without terminatingthe modem session inasmuch as handset 312 and modem 310 enjoy the sameRJ-11 connection to the telephone line. Notwithstanding the fact thatthe modem session may be terminated when an extension telephone set goesoff hook, it may nonetheless be desirable to detect the off hookcondition of an extension telephone set during a modem connection, asdescribed below in conjunction with FIG. 7, so that the PC user may beapprised of the reason for the termination of his modem connection; thatis, it may be desirable for the PC to signal the PC operator that theconnection is terminated because of an off hook condition at anextension, so that the PC operator does not erroneously presume that theconnection was terminated because of an ISP failure, hard drive failure,line failure, or some other reason.

Referring now to FIG. 7, the loop current sense (LCS) circuit 217 ofcurrent sink 216 is suitably employed to detect an extension off hookcondition when the modem is off hook, i.e., during a modem connection.The loop current sense circuit 217 suitably comprises an opto-isolatorelement 704 configured to generate an output signal 706 indicative ofthe state of loop current sense detector circuit 217. More particularly,the output of opto-isolator 704 is suitably pulled high (i.e., pulled toV_(cc)). Thus, when modem off hook relay 214 is open, i.e., when themodem is in the on hook condition, output signal 706 is suitably high.When the modem goes off hook, relay 214 closes, producing a current flowthrough the opto-isolator 704, thereby driving output signal 706 low.With momentary reference to FIG. 8, output signal 706 is suitably highprior to time t_(A), i.e., while the modem is on hook. When the modemgoes off hook at time t_(A), output signal 706 drops, as describedabove. If the modem thereafter stays off hook, it is desirable to detectwhen an extension telephone device goes off hook while the modem remainsin the off hook condition.

With continued reference to FIGS. 2 and 7-8, time t_(B) suitablycorresponds to an extension telephone device going off hook while themodem remains off hook. Surprisingly, output signal 706 goes back high,even though the modem remains off hook (i.e., even though relay 214remains closed). Of course, if the modem were to go back on hook, i.e.,if relay 214 were to open, output signal 706 would also go back to thehigh condition, inasmuch as the current would stop flowing throughopto-device 704, thereby driving output signal 706 high.

As alluded to above, output signal 706 is nonetheless driven back to thehigh state when an extension telephone device goes off hook while themodem remains off hook. More particularly, if the modem is off hook butall other extensions on the same telephone line are on hook, the modemwill generally draw a substantially constant current, for example on theorder of 30 milliamps. If an extension telephone device then goes offhook, the combined current drawn by both telephone devices will beapproximately equal to twice the current drawn by either device, but inreality will likely be slightly less than 60 microamps. This isanalogous to the phenomenon one experiences when taking a shower in ahome, whereupon a family member turns on the water in the sink locatedin the same bathroom as the shower. Although the water supply pressure(analogous to voltage) remains substantially constant, and furtheralthough the amount of water coming out of the shower head (analogous tomodem current) is not adjusted, when the water in the sink is turned on(analogous to an extension telephone device going off hook), the persontaking a shower will typically notice a slight reduction in the rate offlow of the shower water.

Thus, although perhaps counter-intuitive, when an extension goes offhook while the modem is off hook, the current level drawn by the modemactually goes down slightly; this reduction in current drawn by themodem causes opto-element 704 to cease activation, thereby sendingoutput signal 706 back high. When the output signal 706 goes back high,as shown in FIG. 8, this is detected by event detector circuit 218.

In accordance with a preferred embodiment of the present invention,extension on/off remote hangup detector circuit 218, upon detecting thereturn of output signal 706 to the high state, can effectivelydiscriminate between: (i) output signal 706 returning to the high stateas a result of the modem going back on hook; and (ii) output signal 706going back to the high state as a result of an extension telephonedevice going back on hook. In accordance with a particularly preferredembodiment of the present invention, extension detection circuit 218 mayeffectively discriminate between the aforementioned conditions based on,for example, an output signal generated from relay circuit 214 whichaffirmatively indicates whether the modem is on hook or off hook. Inparticular, if output signal 706 returns to the high state and the modemremains off hook, DAA 202 may suitably conclude that the return ofsignal 706 to the high state resulted from an extension telephone devicegoing back on hook. If, on the other hand, signal 706 returns to thehigh state and it is determined that off hook relay circuit 214 wasrecently opened, DAA 202 may suitably conclude that the return of signal706 to the high state resulted from the modem going back on hook asopposed to resulting from an extension telephone device going back onhook.

In accordance with a further aspect of the present invention, extensionon/off remote hangup circuit 218 is also suitably configured to detect aremote hangup condition, i.e., when the telephone device initiating anincoming call hangs up. More particularly, when the remote telephonedevice hangs up, the CO typically interrupts the DC component of theincoming signal for a brief period, for example on the order of 180 to200 milliseconds. During this brief window of a DC null condition, thecurrent loop line 222 goes idle. This idle condition may be suitablydetected by LCS circuit 217, for example as described above. When achange in state in the output of LCS circuit 217 is effected as a resultof a remote hangup event, detector circuit 218 may be suitablyconfigured to discriminate among the various possible causes of a changein state of the output signal produced by LCS circuit 217.

More particularly, a change in state of the output of LCS circuit 217could be caused by the DC null occasioned by a remote hangup, anextension off hook condition while the modem is off hook, or a return ofan off hook modem to the on hook condition, as discussed above. Bytracking the state of the modem (i.e., either on hook or off hook) andof the off hook/on hook condition of extension telephone devices, DAA202 may suitably infer whether a change in state of the output of LCS217 is attributable to a remote hangup or, alternatively, to anotherevent.

In accordance with an alternate embodiment, remote hangup detectorcircuit 218 may also be configured to detect a remote hangup conditionby detecting the presence of a DC null condition in current loop 222 foran anticipated window in the range of 180 to 200 milliseconds. This maybe conveniently implemented in various ways using software, for exampleusing a counter or other convenient technique. In addition, detectorcircuit 218 may be configured to detect the DC null condition via ahardware implementation, for example by detecting a low voltagecondition (corresponding to the DC null interval), and thereafter areturn to a higher relative voltage condition upon termination of the DCnull condition.

In yet a further embodiment, detector circuit 218 may be configured todetect a remote hangup condition by detecting a reversal in the polarityof the V_(tr). That is, many COs signal a remote hangup by reversing thetip-to-ring polarity, either in lieu of or in addition to a briefcessation of the DC signal. In this case, detector circuit 218 may besuitably configured to search for a polarity reversal, for example bydetecting a zero crossing of the DC voltage in current loop 222.

While the present invention has been described with reference to certainpreferred embodiments, it will be appreciated that varioussubstitutions, changes, modifications, omissions, and enhancements maybe made without departing from the spirit thereof. For example, thecircuit elements shown in the Figures are illustrative of the invention,but those skilled in the art will appreciate that the functionalitydescribed herein may be implemented in virtually any convenient manner.Accordingly, it is intended that the scope of the present invention notbe limited by such a description but be fully coextensive with thebroadest interpretation allowable for the appended claims.

I claim:
 1. A method for detecting a number of events associated with anincoming telephone line, a modem associated with said incoming telephoneline, and an extension telecommunication device associated with saidincoming telephone line, said method comprising the steps of:providing adata access arrangement (DAA) device as an interface between said modemand said incoming telephone line; monitoring, with said DAA device, avoltage and a current associated with said incoming telephone line;detecting, in response to changes in said voltage and said current, anoff-hook state and an on-hook state of said extension telecommunicationdevice regardless of whether said modem is in an on-hook or an off-hookstate, said detecting step being performed by said DAA device;generating an output signal indicative of said off-hook state of saidextension telecommunication device, said output signal being generatedby said DAA device for use by said modem; detecting a hang-up state of aremote telecommunication device configured to communicate with said DAAdevice over said incoming telephone line; and discriminating betweenon-hook/off-hook events related to said modem, said extensiontelecommunication device, and said remote telecommunication device, saiddiscriminating step being performed when said modem is in an off-hookstate.
 2. A method according to claim 1, further comprising the step ofgenerating an output report for use by a computing device operativelyconnected to said modem, said output report indicating said hang-upstate of said remote telecommunication device.
 3. A data accessarrangement (DAA) device for interfacing a modem with an incomingtelephone line of the type including a tip node and a ring nodecharacterized by a tip-to-ring voltage V_(tr), said DAA comprising:abridge circuit interposed between said ring node and said tip node;aline-in-use circuit connected to said bridge circuit, said line-in-usecircuit being configured to detect an off-hook state of an extensiontelecommunication device, to detect when said extensiontelecommunication device is returned to an on-hook state, and to operatewhen said modem is in an on-hook state; an on-hook/off-hook relayconnected to said bridge circuit; a line current sense (LCS) circuitconnected to said on-hook/off-hook relay, said LCS circuit beingconfigured to detect said off-hook state of said extensiontelecommunication device and a hang-up state of a remotetelecommunication device when said modem is off-hook, wherein said LCScircuit is further configured to detect when said extensiontelecommunication device is returned to said on-hook state; anda currentsink circuit connected to said LCS circuit.
 4. A DAA device according toclaim 3, wherein:said on-hook/off-hook relay is in a closed position andsaid current sink circuit draws a current from said bridge circuitthrough said on-hook/off-hook relay when said modem is in an off hookstate; and said LCS circuit is configured to detect changes in saidcurrent between said on-hook/off-hook relay and said current sinkcircuit, wherein said changes in said current are responsive to changesin said off-hook and on-hook states of said extension telecommunicationdevice and said hang-up state of said remote telecommunication device.5. A DAA device according to claim 4, further comprising an extensionon/off and remote hang-up detection (ERHD) circuit connected to said LCScircuit, said ERHD circuit being configured to discriminate between saidchanges in said current resulting from said off-hook and on-hook statesof said extension telecommunication device from said changes in saidcurrent resulting from said hang-up state of said remotetelecommunication device.
 6. A data access arrangement (DAA) device forinterfacing a modem with an incoming telephone line of the typeincluding a tip node and a ring node characterized by a tip-to-ringvoltage V_(tr), said DAA comprising:a bridge circuit interposed betweensaid ring node and said tip node; a line-in-use circuit connected tosaid bridge circuit, said line-in-use circuit being configured to detectan off-hook state of an extension telecommunication device, to detectwhen said extension telecommunication device is returned to an on-hookstate, and to operate when said modem is in an on-hook state; a voicerelay circuit, wherein said voice relay circuit shares a connection tosaid incoming telephone line with said modem; and a localtelecommunication device connected to said voice relay circuit, whereinsaid voice relay circuit connects said local telecommunication device tosaid incoming telephone line when said modem is in a data and fax mode,and said line-in-use circuit is configured to detect an off-hook stateof said local telecommunication device and to detect when said localtelecommunication device is returned to an on-hook state.
 7. A DAAdevice according to claim 6, further comprising:a voice hybrid circuitconnected to said voice relay circuit, wherein said voice relay circuitconnects said voice hybrid circuit to said local telecommunicationdevice when said modem is in a voice, telephone answering machine, orspeaker phone mode; a loop current sense (LCS) circuit connected betweensaid voice hybrid and said voice relay circuit, wherein said LCS circuitis configured to detect an off-hook state of said localtelecommunication device, and said LCS circuit is configured to detectwhen said local telecommunication device is returned to an on-hookstate; and and a handset power supply circuit connected to said LCScircuit.
 8. A data access arrangement (DAA) device for connecting amodem to an incoming telephone line, said DAA device comprising:a bridgecircuit connected to said incoming telephone line; a current sinkcircuit connected to said bridge circuit; and a first line current sense(LCS) circuit connected between said bridge circuit and said currentsink circuit, said first LCS circuit being configured to produce anoutput signal indicative of an off-hook state or an on-hook state of anextension telecommunication device and indicative of a hang-up state ofa remote telecommunication device, wherein said first LCS circuit isconfigured to operate when said modem is in an off-hook state.
 9. A DAAdevice according to claim 8, wherein:said current sink circuit draws aDC loop current flow from said incoming telephone line through saidbridge circuit when said modem is in said off-hook state, and said firstLCS circuit is configured to detect changes in said DC loop current,wherein said changes in said DC loop current are responsive to changesin said off-hook and on-hook states of said extension telecommunicationdevice and said hang-up state of said remote telecommunication device.10. A DAA device according to claim 9, wherein said DC loop currentbetween said bridge circuit and said current sink is at a first levelwhen said extension telecommunication device is in said on-hook stateand at a second level, lower than said first level, when said extensiontelecommunication device is in an off-hook state.
 11. A DAA deviceaccording to claim 9, wherein said first LCS circuit comprises anopto-isolator configured to produce said output signal, wherein saidoutput signal is high when said modem is in said on-hook state, highwhen said modem is in said off-hook state and said extensiontelecommunication device is in said off-hook state, and low when saidmodem is in said off-hook state and said extension telecommunicationdevice is in said on-hook state.
 12. A DAA device according to claim 9,further comprising an extension on/off and remote hang-up detection(ERHD) circuit connected to said first LCS circuit, wherein said ERHDcircuit is configured to discriminate between said changes in said DCloop current resulting from off-hook and on-hook states of saidextension telecommunication device and said hang-up state of said remotetelecommunication device.
 13. A DAA device according to claim 12,wherein said ERHD circuit is configured to detect an interruption insaid DC loop current between said bridge circuit and said current sink,wherein said interruption in said DC loop current is for a period oftime.
 14. A DAA device according to claim 13, wherein said EHRD circuitis configured to detect the presence of a DC null condition in said DCloop current for said period of time, wherein said period of time iswithin the range of 180 to 200 milliseconds.
 15. A DAA device accordingto claim 8, further comprising a line-in-use circuit connected to saidbridge circuit, said line-in-use circuit being configured to produce afirst output signal indicative of an on-hook state of said extensiontelecommunication device and a second output signal indicative of anoff-hook state of said extension telecommunication device, wherein saidline-in-use circuit is configured to operate when said modem is in anon-hook state.
 16. A DAA device according to claim 8, furthercomprising:a voice relay circuit coupled to said incoming telephoneline; a local telecommunication device coupled to said voice relaycircuit; a voice hybrid circuit coupled to said voice relay circuit; anda second LCS circuit operatively coupled between said voice hybridcircuit and said voice relay circuit, said second LCS circuit beingconfigured to detect an off-hook state of said local telecommunicationdevice and to detect when said local telecommunication device isreturned to an on-hook state, wherein said voice relay circuit connectssaid local telecommunication device to said voice hybrid circuit andsaid second LCS circuit when said modem is in a voice mode, a telephoneanswering machine mode, or a speaker phone mode.
 17. A DAA deviceaccording to claim 16, wherein:said voice relay circuit connects saidlocal telecommunication device to said incoming telephone line anddisconnects said local telecommunication device from said voice hybridcircuit and said second LCS circuit when said modem is in a data and faxmode; and said line-in-use circuit is configured to detect an off-hookstate of said local telecommunication device and to detect when saidlocal telecommunication device is returned to an on-hook state.
 18. Adata access arrangement (DAA) device for interfacing a modem with anincoming telephone line, said DAA comprising:a bridge circuit connectedto said incoming telephone line; an on-hook/off-hook relay connected tosaid bridge circuit; a current sink circuit connected to saidon-hook/off-hook relay; and means for detecting an on-hook state and anoff-hook state of an extension telecommunication device regardless ofwhether said modem is in an on-hook state or an off-hook state, whereinsaid means for detecting is configured to detect a hang-up state of aremote telecommunication device when said modem is in an off-hook state.19. A DAA device according to claim 18, wherein said means for detectingcomprises:a line-in-use circuit connected to said bridge circuit, saidline-in-use circuit being configured to detect said off-hook state andsaid on-hook state of said extension telecommunication device when saidmodem is in said on-hook state; a line current sense (LCS) circuitconnected between said on-hook/off-hook relay and said current sinkcircuit; and an extension on/off and remote hang-up detection (ERHD)circuit connected to said LCS circuit, wherein said LCS circuit and saidERHD circuit are configured to detect said off-hook state and saidon-hook state of said extension telecommunication device and saidhang-up state of said remote telecommunication device when said modem isin an off-hook state.
 20. A DAA device according to claim 19,wherein:said on-hook/off-hook relay is in an open position and said LCScircuit and said ERHD circuit are inoperative when said modem is in saidon-hook state; and said line-in-use circuit detects changes in voltagesin said incoming telephone line indicative of said off-hook state andsaid on-hook state of said extension telecommunication device when saidmodem is in said on-hook state.
 21. A DAA device according to claim 19,wherein:said on-hook/off-hook relay is in a closed position and saidcurrent sink draws a current from said incoming telephone line throughsaid bridge circuit when said modem is in said off-hook state; said LCScircuit and said ERHD circuit detect changes in said current from saidincoming telephone line to said current sink indicative of said off-hookstate and said on-hook state of said extension telecommunication deviceand said hang-up state of said remote telecommunication device when saidmodem is in said off-hook state.